It is known to laminate at least partially transparent films onto one side of openings formed into and through security paper substrates, for instance from International (PCT) Publications Nos. WO 2008/104904 A1, WO 2009/112989 A1 and WO 2010/001317 A1 in the name of the present Applicant (which publications are all incorporated herein by reference in their entirety), for the purpose of creating at least partially transparent windows in such security paper substrates. The laminated film serves multiple purposes, including acting as a means to close one side of the opening that is formed into and through the substrate, as well as a means to allow optional filling of the opening with a transparent filling material.
The lamination of the at least partially transparent films however necessitates a dedicated processing step which increases production costs.
An alternate solution is therefore required with a view to create a transparent window in a security substrate.